This piece in today's Times highlights the issue – quoting Joe Nikruto, a senior commodities broker at RJO Futures: "It is looking bleak in the Midwest at the moment and unless we get some rain we are talking more crop reductions in the future. We have got 48 hours before we start seeing significant damage."

This is already having an impact in commodities markets. Rodolphe Roche, manager of the Schroder AS Agriculture Fund, says: "After having been experiencing a lower trend since mid-2011, corn prices rebounded overwhelmingly in the last month due to crop concerns caused by the heat wave in the US Midwest… The other grains markets (wheat and oats in particular) rose strongly in the wake of corn prices. The summer months in the northern hemisphere are a critical period for spring crop yields, and as a result volatility is often high. In terms of positioning, we increased temporarily our allocations in this sub-sector over the last few weeks."

The knock-on effects of higher corn prices could be severe: Corn is a key feed stock and the rising prices are expected to push up the cost of chicken, beef and pork.

The severe weather conditions in the MidWest are also having an effect on oilseeds markets where, Roche says, expectations of large crop losses in the US, coupled with a poor soybean harvest in Latin America this winter due to lack of rain, along with sustained Chinese import pace of oilseeds, should push up prices.

The concern for many is what higher food prices will do to the outlook for global growth; they are a key component of inflation. There has been an expectation that inflation will fall as oil prices move lower, but this may reverse that positive effect.

The topic was widely discussed at the time of the last surge in agricultural commodities. In 2011, Goldman Sachs dismissed any imminent threat from high food prices, but this conclusion was widely refuted in some quarters. For example, this piece on Zerohedge says : "After ignoring the topic of surging food prices, head economist Andrew Tilton finally decides to discuss the issue (following 5 countries with violent riots demanding to learn much more about the issue). Not surprisingly the conclusion is one that will not make any dent on the firm's Goldilocks outlook for a QE-inspired, pretend economy…. And what happens if commodity prices do not stabilize "relatively soon", which they won't as long as Ben Bernanke continues to step in for the increasingly sparser foreign Treasury purchasing interest."

Clearly some places are affected more profoundly by rising food prices than others. In particular, emerging markets tend to suffer disproportionately from rising food prices because they form a greater part of household spending. Overall, it would seem naïve to dismiss the potential for further shocks as a result of the weather in the Midwest.